The present disclosure relates to additive manufacturing and, more particularly, to a core with an additively manufactured portion for use in casting an internal cooling circuit within a gas turbine engine component.
Gas turbine engines typically include a compressor section to pressurize airflow, a combustor section to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases. Gas path components, such as turbine blades, often include airfoil cooling that may be accomplished by external film cooling, internal air impingement, and forced convection either separately or in combination.
One way to improve airfoil cooling efficiency is by increasing the pressure and temperature of the compressed and combusted air, from which the turbine extracts work. Thus, more highly-evolved turbines see ever-increasing gaspath and cooling air temperatures, which may present a challenge as the gaspath temperatures often exceed the incipient melting temperatures of the airfoils', combustor liners', and BOAS' constituent alloys. Complex internal cooling schemes must be relied upon to supply convective cooling and source film cooling, which are most often produced by investment casting of superalloys with ceramic cores. The film cooling holes are later subtractively drilled through a variety of methods, which on high pressure airfoils, may number between 10 and 300.
Cast-in cooling holes have been demonstrated in single crystal, at least on flat plates, and have not exhibited significant signs of recrystallization. But there are issues with the process. The fragility of ceramic cores, whether traditionally made through injection or molding, or via ceramic additive manufacturing, does not lend itself to the casting of cooling holes which may be as small as 0.014″ in diameter for some portion of the hole. Insertion of a multitude of quartz/alumina rods (which are stronger) or refractory metal pins into a ceramic core (either pre- or post-injection) is not a producible concept, either, as this quickly becomes cost and time prohibitive and is likely not a repeatable process for shaped holes.